1) Field of the Invention
The present invention relates to a phase control method and system for, when manufacturing a corrugated fiberboard sheet composed of a plurality of corrugated core paper layers, controlling a phase shift between the core paper.
2) Description of the Related Art
FIG. 6 is a cross sectional view showing a corrugated fiberboard sheet comprising a plurality of (for example, 2) core paper layers, and a double-faced corrugated fiberboard sheet S shown in FIG. 6 is made by adhering core paper C.sub.1, C.sub.2 constituting two layers to each other in a laminated (piled-up) condition between a pair of upper and lower liners L.sub.1, L.sub.2. The two core paper C.sub.1, C.sub.2 have crests (mountains) different in heights H.sub.1, H.sub.2 (&gt;H.sub.1) from each other, respectively, with the crests forming corrugated configurations with the same pitch P.sub.o.
Referring to FIG. 7, a description will be made hereinbelow of an apparatus for manufacturing the double-faced corrugated fiberboard sheet S shown in FIG. 6.
FIG. 7 is a side elevational view illustratively and schematically showing a construction of a common corrugated fiberboard sheet manufacturing apparatus for manufacturing a double-faced corrugated fiberboard sheet S comprising two core paper C.sub.1, C.sub.2 layers.
In FIG. 7, omitted is a first single facer for manufacturing a single-faced corrugated fiberboard sheet S.sub.1 in a manner that the first core paper C.sub.1 shaped into a corrugated configuration is adhered onto the liner L.sub.1, but shown is a second single facer SF2 for manufacturing a two-layer core single-faced corrugated fiberboard sheet S.sub.2 in a manner of adhering the second core paper C.sub.2 having a corrugated configuration with the same pitch as that of the first core paper C.sub.1 onto the single-faced corrugated fiberboard sheet S.sub.1 in a laminated condition, and further shown is a double facer DF for manufacturing a double-faced corrugated fiberboard sheet S in a way of adhering the liner L.sub.2 onto the two-layer core single-faced corrugated fiberboard sheet S.sub.2 manufactured by the second single facer SF2.
The second single facer SF2 is composed of guide rolls 1, 2, preheating rolls 3, 4, an endless pressure belt 5, drive rolls 6, 7, an upper roll 8, a lower roll 9, a paste reservoir 10 and paste applying rolls 11, 12.
The guide rolls 1, 2 and the preheating rolls 3, 4 are for the purpose of guiding the single-faced corrugated fiberboard sheet S.sub.1 coming from the non-shown first single facer to between the pressure belt 5 and the upper roll 8, while the preheating rolls 3, 4 also have a function to preheat the single-faced corrugated fiberboard sheet S.sub.1.
The endless pressure belt 5 is wound around the drive rolls 6, 7 to be rotationally driven therethrough. In addition, the upper roll 8 is placed into contact with the endless pressure belt 5 stretched between the drive rolls 6, 7 to pressurize it from the below. Moreover, under the upper roll 8, there is disposed the lower roll 9 for shaping the second core paper C.sub.2 into a corrugated configuration in a manner that the second core paper C.sub.2 is put between the upper roll 8 and the lower roll 9.
The paste reservoir 10 holds a paste to be used for adhering the second core paper C.sub.2 onto the single-faced corrugated fiberboard S.sub.1, and the paste applying rolls 11, 12 apply the paste within the paste reservoir 10 onto peak portions of the crests of the second core paper C.sub.2 shaped into a corrugated configuration in a manner of being put between the upper roll 8 and the lower roll 9.
Between the endless pressure belt 5 and the upper roll 8, there is interposed the single-faced corrugated fiberboard S.sub.1, and at the same time, there is put the second core paper C.sub.2 shaped into a corrugated configuration between the upper roll 8 and the lower roll 9 and undergoing the paste application. In this way, the second core paper C.sub.2 is pasted on the single-faced corrugated fiberboard sheet S.sub.1, thus manufacturing the two-layer core single-faced corrugated fiberboard sheet S.sub.2.
Furthermore, the second single facer SF2 is provided with a tension adjusting unit 17 for adjusting a tension to be given to the single-faced corrugated fiberboard sheet S.sub.1. The tension adjusting unit 17 is, for example, made up of a suction box (not shown) for sucking the single-faced corrugated fiberboard sheet S.sub.1 from the liner L.sub.1 side, with the tension to the single-faced corrugated fiberboard sheet S.sub.1 being adjusted by the adjustment of that suction force (the frictional resistance force for the single-faced corrugated fiberboard sheet S.sub.1).
In addition, provided is a pulse sensor 22 for sensing, as a pulse signal, the crests of the first core paper C.sub.1 of the single-faced corrugated fiberboard sheet S.sub.1 to be interposed between the endless pressure belt 5 and the upper roll 8, and further provided is a pulse sensor 23 for sensing, as a pulse signal, the crests of the second core paper C.sub.2 to be put between the endless pressure belt 5 and the upper roll 8. These pulse sensors 22, 23 constitute a phase shift measuring unit 18 for measuring a phase shift quantity .delta. between the crests of the first core paper C.sub.1 and the crests of the second core paper C.sub.2.
On the basis of the phase shift quantity .delta. measured by the phase shift measuring unit 18, a tension control unit 19 controls the tension to the single-faced corrugated fiberboard sheet S.sub.1 through the tension adjusting unit 17 so that the phase shift quantity .delta. becomes zero. An tension control operation by this tension control unit 19 will be described herein later with reference to FIGS. 8 and 9.
Incidentally, in fact, the tension control unit 19 adjusts the suction force to the single-faced corrugated fiberboard sheet S.sub.1 caused by the suction box organizing the tension adjusting unit 17, so that the single-faced corrugated fiberboard sheet S.sub.1 is adjustable to achieve the adjustment of the phase of the first core paper C.sub.1 on the single-faced corrugated fiberboard sheet S.sub.1 side.
On the other hand, the two-layer core single-faced corrugated fiberboard sheet S.sub.2 manufactured by the second signal facer SF2 is guided by the guide rolls 13a, 13b toward a double facer DF. This double facer DF is composed of pressure rolls 15, 16, and the two-layer core single-faced corrugated fiberboard sheet S.sub.2, together with the liner L.sub.2 guided by a guide roll 14, is placed between the pressure rolls 15, 16, thus manufacturing the double-faced corrugated fiberboard sheet S.
In the corrugated fiberboard sheet manufacturing apparatus thus constructed, the single-faced corrugated fiberboard sheet S.sub.1 produced by the first single facer (not shown) is conveyed through a path (not shown) to the second single facer SF2.
In this second single facer SF2, the single-faced corrugated fiberboard sheet S.sub.1 is guided by the guide rolls 1, 2 and the preheating rolls 3, 4 to be delivered to between the pressure belt 5 and the upper roll 8. The single-faced corrugated fiberboard sheet S.sub.1 is preheated when passing through the outer circumferences of the preheating rolls 3, 4.
On the other hand, the second core paper C.sub.2 is shaped into a corrugated configuration when passing through between the upper roll 8 and the lower roll 9 in a state of being interposed therebetween, and after a paste is applied onto the crest peak portions of the corrugated configuration by means of the paste applying rolls 11, 12, the second core paper C.sub.2, together with the single-faced corrugated fiberboard sheet S.sub.1, is conveyed to between the pressure roll 5 and the upper roll 8. Further, the single-faced corrugated fiberboard sheet S.sub.1 and the second core paper C.sub.2, being in a laminated condition, are subjected to given heating and pressing force, so that the second core paper C.sub.2 is adhered onto with the single-faced corrugated fiberboard sheet S.sub.1, thereby manufacturing the single-faced corrugated fiberboard sheet S.sub.2. In this case, the crests of the second core paper C.sub.2 are formed to have a height higher than that of the crests of the first core paper C.sub.1.
At this time, the phase shift measuring unit 18 measures the phase shift quantity .delta. between the corrugated configuration of the first core paper C.sub.1 of the single-faced corrugated fiberboard sheet S.sub.1 and the corrugated configuration of the second core paper C.sub.2 to be adhered to the first core paper C.sub.2 and feedbacks the phase shift quantity .delta. being the detection results of the pulse sensors 22, 23 to the tension control unit 19 which in turn, adjusts the tension to the single-faced corrugated fiberboard sheet S.sub.1 through the use of the tension adjusting unit 17.
Referring to FIGS. 8A to 8C, a description will be taken hereinbelow of a prior method of calculating a sheet tension changing quantity on the basis of the phase shift quantity .delta. measured.
If a phase shift quantity .delta..sub.2 is obtained as the present measured value as shown in FIG. 8A, a sheet distortion quantity .DELTA..epsilon.*.sub.1 for setting the phase shift quantity .delta. to zero is obtained as shown in FIG. 8B. Subsequently, as shown in FIG. 8C, the distortion quantity .DELTA..epsilon.*.sub.1 is divided by a sheet distortion quantity K per a tension of 1 kgf/cm so that a sheet tension changing quantity .DELTA.T.sub.1 for the correction (or modification) of the phase shift is calculated as .DELTA..epsilon.*.sub.1 /K.
In this case, a phase shift occurs by .DELTA.a during a measurement interval L from the measurement of the phase shift quantity .delta..sub.2 to the measurement of the next phase shift quantity .delta..sub.3. Accordingly, even if adding the aforesaid sheet tension changing quantity .DELTA.T.sub.1, the next phase shift quantity .delta..sub.3 does not reach zero, but assumes a quantity .delta..sub.3 (=-.DELTA.a) shifted by the phase shift quantity .DELTA.a from zero. As shown in FIG. 8A, the phase shift quantity .DELTA.a takes place at a given inclination even in the case of not conducting the phase control, and in the case of no phase control, the phase shift quantity .DELTA.'.sub.3 after the elapse of the measurement interval L comes to .delta..sub.2 -.DELTA.a.
Referring to the flow chart (steps T1 to T4) of FIG. 9, a description will be made hereinbelow of a phase control procedure based upon the above-mentioned sheet tension changing quantity calculating method.
First, for instance, if the phase shift quantity .delta..sub.2 shown in FIG. 8A is measured as the present measured value by the measuring unit 18 (the pulse sensors 22, 23) (step T1), the tension control unit 19 decides whether or not the phase shift quantity .delta..sub.2 is within an allowable range (step T2). If being within the allowable range (YES route from step T2), the operational flow returns to the step T1 to perform the next measurement after the elapse of the phase shift measurement interval L.
On the contrary, if the present phase shift quantity .delta..sub.2 is out of the allowable range (NO route from step T2), the tension control unit 19 calculates the phase shift correction sheet tension changing quantity .DELTA.T.sub.1 as .DELTA..epsilon.*.sub.1 /K as mentioned above with reference to FIG. 8C (step T3), and controls a braking unit 21 constituting the tension adjusting unit 17 by a quantity corresponding to the tension changing quantity .DELTA.T.sub.1 to alter the tension to the single-faced corrugated fiberboard sheet S.sub.1 (step T4).
Besides, the phase shift quantity .delta..sub.1 shown in FIG. 8A represents an example of phase shift quantities immediately before the phase control by the repetitions of the steps T1 to T4 shown in FIG. 9, and is shown for the purpose of facilitating the comparison with a phase control method according to an embodiment of this invention which will be described herein later with reference to FIGS. 1A to 1C, and in this case, the phase control is not conducted on the basis of the phase shift quantity .delta..sub.1.
The phase shift occurs due to the difference between the crest pitches of the core paper C.sub.1 and the core paper C.sub.2. That is, as shown in FIG. 10, if the crest pitch P.sub.2 of the core paper C.sub.2 is smaller than the crest pitch P.sub.1 of the core paper C.sub.1, a phase shift +.delta. occurs, with the result that a shift between the corrugated configurations of the core paper C.sub.1 and the core paper C.sub.2 takes place when being piled up on each other. On the other hand, as shown in FIG. 11, if the crest pitch P.sub.2 of the core paper C.sub.2 is larger than the crest pitch P.sub.1 of the core paper C.sub.1, a phase shift -.delta. occurs, with the result that a shift between the corrugated configurations of the core paper C.sub.1 and the core paper C.sub.2 also takes place when being piled up on each other.
When the above-mentioned shift between the corrugated configurations of the core paper C.sub.1 and the core paper C.sub.2 takes place in bonding them together, difficulty is experienced to appropriately adhere the core paper C.sub.1 and the core paper C.sub.2 to each other, which makes it difficult to form an appropriate single-faced corrugated fiberboard sheet S.sub.2.
Thus, a corrugated fiberboard sheet including a plurality of core paper layers which are appropriately adhered to each other can not fulfill the original function of the corrugated fiberboard sheet with a plurality of core paper layers for the cushioning effect and strength increase, and is defective as a product.
For this reason, as described with reference to FIGS. 8A to 8C and 9, in a manner of measuring the phase shift quantity .delta. to adjust the tension to the single-faced corrugated fiberboard S.sub.1 on the basis of the phase shift quantity .delta., the phase shift feedback control is done.
However, as also mentioned before with reference to FIGS. 8A to 8C, in the case of the prior phase control method, since the tension changing quantity .DELTA.T.sub.1 for the correction of the present phase shift quantity .delta..sub.2 (putting it to zero) is simply calculated using only the present phase shift quantity .delta..sub.2 by the current measurement, a phase shift occurs during the tension alteration (the measurement interval L), with the result that it is difficult to completely correct the phase shift.
More specifically, since the phase shift occurs by .DELTA.a during the measurement interval L (that is, during the tension alteration) from the time of the measurement of the phase shift quantity .delta..sub.2 to the time that the next phase shift quantity .delta..sub.3 is measured as the present measured value .delta..sub.2, even if adding the tension changing quantity .DELTA.T.sub.1 calculated as .DELTA..epsilon.*.sub.1 /K, the next phase shift quantity .delta..sub.3 does not come to zero, but shifts by the phase shift quantity .DELTA.a from zero, which makes it difficult to fully correct the phase shift.